Buzzer in rear hatch area???

Took out my 2002 Odyssey last weekend and had this intermittent high pitched buzzer go off in the rear hatch area once I put the vehicle in drive. It was steady at first, then go off and on when I hit a bump on the road. I checked the hatch several times and it was secure. After driving it over the weekend the buzzer has completely stopped. I didn't see any reference to it in the manual. Does anyone know what this is? I'll be bringing it in for servicing shortly. Thanks for your help.